New York City police officers shot and killed a black man who was known to be mentally ill on a Brooklyn street corner on Wednesday afternoon after he pointed what the officers believed was a gun at them, the authorities said. The object, however, turned out to be a metal pipe with a knob on it.

The shooting drew a tense, charged crowd of dozens to the streets of Crown Heights. The Police Department had encountered the man before and classified him as emotionally disturbed, and the shooting raised questions about what the officers at the scene knew about him.

Five officers — three of them in street clothes, two in uniform — were responding to three 911 calls about a man threatening people with a silver gun near the corner of Montgomery Street and Utica Avenue in Crown Heights, Terence A. Monahan, the chief of department, said at a news conference. A law enforcement official who listened to one of the calls said a woman was frantically reporting that a man was pointing a gun at people.

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Saheed Vassell was fatally shot by the police in Crown Heights on Wednesday. He was holding a metal pipe that passers-by and officers thought was a gun.CreditCreditTodd Heisler/The New York Times

The police found a man who matched descriptions from the 911 callers, Chief Monahan said.

“The suspect then took a two-handed shooting stance and pointed an object at the approaching officers,” Chief Monahan said.

Chief Monahan said four of the officers — the three in street clothes and one uniformed officer — fired 10 bullets in all. The man, identified by his father as Saheed Vassell, 34, was pronounced dead after being taken to Kings County Medical Center.

In an interview at his home late Wednesday night, Mr. Vassell’s father, Eric Vassell, said his son had bipolar disorder and had been admitted to the hospital multiple times in recent years, sometimes after encounters with the police. The younger Mr. Vassell, who was born in Jamaica and came to the United States when he was 6, lived with his family in a Crown Heights apartment and had worked as a welder. He also had a 15-year-old son.

Mr. Vassell’s father said he had never seen his son act as if he had a gun.

He would “just walk around the neighborhood and help people,” the father said.

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Saheed Vassell

Area residents said Mr. Vassell was a familiar figure on the corner and a caring father who begged for money in a nearby subway station and did odd jobs for shopkeepers. He loved to dance and was widely known to be mentally ill. People said he had a penchant for picking things up off the street — cigarette lighters, empty bottles and other curbside flotsam — and playing with them like toys.

John Fuller, 59, said that he had known Mr. Vassell for years and that local police officers had, too. He echoed a common refrain: The officers should have known him well enough to not simply shoot him to death. “Every cop in this neighborhood knows him,” Mr. Fuller said.

The police said he had been arrested before and said officers had classified him as an emotionally disturbed person in previous encounters.

The police released blurry still images from surveillance videos — though not the videos themselves — showing a man with an outstretched arm and something in his hand. The police said the images showed him pointing an object that appeared to investigators to be a gun at people on the street and then pointing it in the officers’ direction after they arrived. They also released a picture of what the man turned out to have been holding: a slim, curved silver pipe with a cylindrical knob at the end of it.

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The Police Department said the man was in “a two-handed shooting stance” and brandishing an object at responding officers when they shot him.CreditNew York Police Department

Witnesses said the police officers appeared to fire almost immediately after they got to the corner around 4:45 p.m. Some of the witnesses said they did not hear the officers say anything to the man before firing, while another witness said she heard the officers and the man exchange some words.

The police did not answer questions about whether the officers had said anything before firing.

Dozens were still gathered at the scene late Wednesday and tempers flared hours after the shooting. “Murder!” some bystanders shouted at dozens of police officers behind yellow tape. Other crowd members wept at how this had happened on the 50th anniversary of the Rev. Dr. Martin Luther King Jr.’s assassination. Others spoke of wanting to riot. When darkness fell, a group of about 10 protesters arrived carrying Black Lives Matter signs.

The killing held echoes of the shooting less than three weeks ago in Sacramento in which the police shot and killed a black man who they believed was pointing a gun at them, but who, it turned out, was actually holding a cellphone.

On Wednesday in Brooklyn, Jaccpot Hinds, 40, was walking south on Utica Avenue near Montgomery Street when he saw an unmarked police car pass him and pull across two lanes of traffic near where a man was standing on a street corner. Mr. Hinds said a plainclothes officer got out of the passenger seat of the car and fired at the man several times. The officer appeared to shoot him in the neck, chest and right arm, Mr. Hinds said, and then walked over to the man and prodded his chest with the service weapon.

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A tense crowd gathered as the police investigated a fatal shooting in the Crown Heights section of Brooklyn.CreditJohn Taggart for The New York Times

Mr. Hinds said that officer, joined by two other plainclothes officers who had been in the car with him, tried to resuscitate the man.

Chief Monahan said the officers who fired had not been wearing body cameras. He said that the plainclothes officers were part of an anti-crime unit and that the uniformed officers belonged to the Strategic Response Group, which is assigned to major events and hot spots of crime. The names and races of the police officers were not released.

An employee at a beauty salon on the corner, Angie, 52, said she heard the police fire and then saw the man drop. She said the police then fired several more shots before they ran over to the man and handcuffed him.

“We hear the first shot, the guy went down and then they started firing again,” said Angie, who declined to give her last name.

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Officers responded to three 911 calls about a man threatening people with a silver gun near the corner of Montgomery Street and Utica Avenue in Crown Heights, according to Terence A. Monahan, the chief of department.CreditJohn Taggart for The New York Times

Angie described Mr. Vassell as a quiet man who often sat outside near a barbershop and sometimes worked odd jobs at her beauty salon for a few dollars.

“He would just walk and bob his head,” she said. “If we ask him to do our chores, he’d come and do it.”

Rocky Brown, 45, who knew him for years, said he was a friendly man who was mentally ill.

“He’s harmless,” Mr. Brown said. “A very willing guy, a very nice guy, a good guy.”

Betty Weaver, 71, said Mr. Vassell would often greet her when she was on her way to church.

Another woman, Nicole Williams, said she had given him $2 earlier on Wednesday afternoon. His last words to her, she said, were “Thank you, God.”

Matt Stevens contributed reporting. Doris Burke contributed research.

A version of this article appears in print on , Section A, Page 25 of the New York edition with the headline: Police in Brooklyn Kill a Man Pointing a Pipe Believed to Be a Gun. Order Reprints | Today’s Paper | Subscribe